This invention is a unique arrangement of a plating device for electroplating work pieces with metallic deposits. It is often desirable to process the work pieces using conveyorized equipment. When the work pieces are flat sheets or plates with through holes, such as printed circuit boards, they are often processed through operations in which solutions are forced through the holes. Examples of this include: drilling smear removal, drilling burr residue removal, applying materials to hole walls to make nonconductive hole walls conductive, stripping of metallic deposits from hole walls, and development of coatings out of holes.
The most commonly used conveyorized equipment for such applications has a horizontal roller conveyor on which the work pieces are placed. The work pieces are carried horizontally through processing chambers where solutions are pumped or sprayed onto the surfaces and into the through holes. Other less common processing equipment has a conveyor with vertical rollers. The vertical rollers are usually accompanied by horizontal guide wires or rails to keep the work pieces vertical while being transported through the processing chambers. Inside the processing chambers, solutions are pumped or sprayed onto the surfaces and into the through holes.
Up to this time, it has been common practice to process work pieces through several operations using conveyorized equipment to prepare them for plating of metallic deposits onto essentially the entire planar surface and the surfaces of the through holes. Even though conveyorized equipment is used for many manufacturing steps prior to electroplating, in order to perform the actual plating operation, the work pieces are usually removed from the conveyorized equipment, attached to electrically conductive racks, and electroplated in dip tanks. Even when conventional automated plating machines are used to transport the work pieces through the plating tanks for the electroplating operation, it is still necessary to unload work pieces from the conveyorized equipment and manually place them onto the rack of the automated plating machine. It is desirable to plate the work pieces as they are transported through the conveyorized equipment. Such in line plating, without removing the work pieces from the conveyorized equipment, would reduce processing time and labor.
Automatic plating machines originally designed for decorative or engineering electroplating which transport parts through dip tanks on carousels or programmed hoists have been used to successfully plate flat work pieces with through holes. However, this type of plating equipment is not well suited to other manufacturing operations where solutions must be sprayed or pumped through the holes in the work pieces. This is especially true when the diameter of the holes is small in relation to the thickness of the panels. For these non-plating operations, the work pieces are usually processed in conventional horizontal conveyorized equipment or vertical conveyorized equipment described above.
Automatic plating machines originally designed to electroplate wire or continuous strips of metal, such as reel to reel plating of electronic component lead frames, are not suitable for use with discreet flat work pieces such as printed circuit boards. Because wire and strips are continuous, they are easily electrified by applying an electric potential difference between convenient points along the work piece. However, flat panels are discreet work pieces rather than continuous strips. The electrification of discreet work pieces is not possible using wire or reel to reel plating machines.
Several conveyorized plating machines for printed circuits boards and other similar work pieces have been developed. Most such conveyorized machines are designed for plating a limited part of the planar surface of the work piece, such as contact tabs. The area on which the plated deposit is applied is usually limited to one or more edges of the panel. Examples of this type of machine are disclosed in U.S. Pat. No. 4,035,245, 4,186,062, and 4,377,461. Whereas these types of machines are well suited for plating the margins of flat work pieces, they are not suitable for plating the entire planar surfaces and the surface of through holes.
Several other plating machines designed to simultaneously plate essentially the entire planar surfaces and the surfaces of through holes of flat work pieces have been proposed. Examples of these include those disclosed in U.S. Pat. No. 4,385,967, 4,401,522, 4,755,271, 5,417,828, and 5,658,441. Whereas machines of these types can successfully plate essentially the entire planar surfaces and the surfaces of through holes of the work pieces, all of these machines have one or more specific problems as will be more fully explained hereinafter.
The apparatus disclosed in U.S. Pat. No. 4,385,967 issued to Brady et al transports the work pieces placed horizontally on a conveyor having horizontal rollers. Using this type of machine, work pieces may be processed through normal nonelectrified operations using conventional horizontal processing equipment mated to the plating apparatus. When work pieces reach the point in the manufacturing operations at which electroplating is required, one edge of each panel engages a series of electrified, driven contact wheels. The contact wheels transport the work pieces through the plating chamber and provide electrical connection to the work pieces. One or more of the electrified contact wheels is in electrical contact with the work piece during the entire time the work piece is in the plating chamber. Whereas this apparatus does allow the continuous processing of work pieces through conventional horizontal conveyorized equipment and through the disclosed apparatus without unloading and reloading, the contact wheels receive undesired electroplated deposits. Although the contact wheels are shielded from the electrolyte solution, they still accumulate electroplated deposit. These accumulated electroplated deposits interfere with electrical contact with the work pieces. When such buildup of electrodeposited metal occurs, the deposit must be removed from the contact wheels. Because of the location of the contact wheels, and because of the design of the wheel driving mechanism, removal of the contact wheels for cleaning is difficult and entails substantial time and labor. Additionally, the work pieces must be carefully positioned so that one edge of each panel is aligned properly to engage with the contact wheels. This need for alignment necessitates use of a repositioning mechanism immediately before the work pieces enter the contact wheel area. Otherwise, work pieces not repositioned immediately before entering the plating zone may not properly engage the electrified contact wheels. Furthermore, the supporting device that carries the edge of the work pieces opposite the contact wheels must be adjusted for each different width panel. All panels processed must have a common width or the machine must be taken out of service while the support device is adjusted for a new panel width. This limitation prevents continuous processing of mixtures of work pieces of significantly different widths. Taking the machine out of service for width adjustments dramatically limits it usefulness for many factories that process work pieces of differing widths. In addition, the contact wheels are offset outside the zone where the electrolyte makes continuous contact with the work pieces. This offset is required to allow space for the shielding to protect the contact wheels from making electrical contact with large volumes of the electrolyte. Such shielding is necessary to minimize electrodeposition of metal onto the contact wheels. However, as disclosed by Brady, the portion of the work piece which contacts the contact wheels, that lies between the contact wheels and the zone where the electrolyte washes over the work piece will not be plated. Thus, the work pieces may have no through holes that require plating in this unusually wide area. This results in wasted materials and added expense. Finally, this apparatus is extremely complex. With so many moving parts that require careful alignment, the maintenance of this apparatus can reasonably be expected to demand substantial time and labor.
The apparatus disclosed in U.S. Pat. No. 4,401,522 issued to Buschow et al is designed to plate essentially the entire surface and through holes of flat work pieces, such as printed circuit boards, while they are transported through the plating zone by a conveyor located about the plating tank. Work pieces are suspended vertically from the conveyor by electrically conductive carriers. Electrical contact with the work pieces is made by electrically conductive clamps attached to the carriers grasping one edge of each work piece. The electrically conductive carriers are attached to the conveyor. The carriers make electrical contact with electrified strips outside the process chambers at appropriate locations. The work pieces are thereby electrified while they are transported through the electroplating process chambers. Work pieces suspended vertically from such a conveyor tend to swing in an arc perpendicular to the direction of travel of the conveyor. If the work pieces swing excessively, the panels may strike the walls of the chambers and/or the vertical spargers inside the process chamber causing the conveyor to jam. If the swinging becomes excessive in the plating zone, the work pieces could strike the metallic anode baskets, creating an electrical short. In addition, this apparatus is not compatible with conventional horizontal conveyorized processing equipment. Work pieces processed on such horizontal equipment must be unloaded and manually clamped onto clamps of the disclosed apparatus. Furthermore, in order to plate essentially the entire surface of the work pieces, the clamps must be exposed to the electrolyte. The clamps accumulate electroplated metallic deposits. The metallic deposits must be removed periodically to assure proper continued operation of the apparatus. Such removal of undesired metallic deposits entails undesirable time and labor. Furthermore, the machine is mechanically complex with many moving parts. It can reasonably be expected to require significant time and labor to maintain the apparatus in proper working order.
The apparatus disclosed in U.S. Pat. No. 4,755,271 issued to Hosten is designed to electroplate plate-shaped work pieces, such as printed circuit boards, in horizontal position as they are conveyed through processing chambers. This type of apparatus exhibits several characteristics that make it undesirable. For example, one or more edges of the work piece are grasped by one or more tong-like clamps. The clamps, attached to a conveyor drive outside the zone in which the electrolyte freely washes over the work pieces, carry the work pieces horizontally through the electroplating chamber. The clamps are electrified to supply electrical current to the work piece. Whereas the design of the clamps and shielding seals is intended to minimize the quantity of electrodeposited metal on the clamps, some metallic deposition does occur. To remove the undesired metallic deposits, Hosten teaches using chemical and/or mechanical stripping of the deposits after each cycle of the clamps through the electroplating chamber. Additionally, the work pieces must be properly positioned on the conveyor for the clamps to properly engage the edge of the panel. Further, some means must be supplied for aligning the panels so the clamps engage the work pieces properly. Huston also teaches that it is often desirable to have two sets of clamps attached to two separate conveyors which operate parallel to the direction of travel of work pieces. The two sets of clamps operating in concert with each other support both edges of the work pieces that are parallel to the direction of travel. Use of a second set of clamps and associated conveyor supports the work pieces more securely, especially when the work pieces are thin and have little rigidity. While this desirable configuration with two parallel conveyors and associated clamps improves the support for the work pieces, it severely restricts the sizes of work pieces that may be processed. If the parallel conveyors are spaced at a fixed distance apart, only work pieces with at least one dimension equal to the fixed distance between the clamps will properly engage both sets of clamps. If the conveyors were arranged so the distance between them is adjustable, work pieces of varying widths could be accommodated. Whenever work pieces with different widths are to be processed, the machine has to be stopped while the adjustments are made. Furthermore, it would be impossible to continuously process a mixture of panels of differing widths. Additionally, because a sealing shield is used to prevent most of the electrolyte from contacting the clamps, a substantial area of the work pieces does not make continuous contact with the electrolyte. Those areas of the work pieces not in contact with electrolyte do not plate. It is therefore impossible to have plated through holes in those areas. This limits the capabilities of the plating apparatus and can result in wasted materials for the work pieces. Further, many of these parts of such devices are subject to wear and maladjustment. The labor and time required to maintain such a complex machine in proper operating condition can reasonably be expected to be quite high.
An apparatus for conveyorized plating of flat components, such as printed circuit boards is disclosed in U.S. Pat. No. 5,417,828 issued to Sergio. This apparatus processes work pieces through the plating cell while they are suspended vertically from a conveyor located above the plating zone. The conductive clamps that support the work pieces are electrified to provide electrical current to the work pieces. The vertical position of the work pieces, as they are transported through the electroplating zone, is not compatible with conventional horizontal processing equipment. In order for this apparatus to be used in conjunction with such horizontal conveyorized processing equipment, the work pieces must be removed from the horizontal equipment and manually clamped onto the conveyor of the disclosed apparatus. Such handling entails undesirable time and labor. Additionally in order to plate the entire surface of the work pieces, the conductive clamps are subject to contact with the electrolyte. The clamps will receive a metallic electrodeposit that will eventually interfere with operation of the clamps. Such metallic deposit must be periodically removed to assure continued operation of the apparatus. Furthermore, work pieces suspended from a vertical clamp tend to swing in an arc perpendicular to the direction of travel of the conveyor. If the swinging becomes excessive, the work pieces can strike the walls of the electrolytic cells. Should that occur, the conveyor could be jammed.
The apparatus disclosed in U.S. Pat. No. 5,658,441 issued to Spain et al is designed to electroplate flat work pieces with through holes, such as printed circuit boards, in a horizontal conveyorized spray plating machine. The electrified clips and/or pusher bars push the work piece through the plating zone. In order for the pusher bars to engage the trailing edge of the work pieces and thereby provide electrical contact with the work pieces, the work pieces must be properly spaced horizontally along the roller conveyor. Should the work pieces be spaced too close together, the pusher bars may attempt to engage the work pieces at a point other than the trailing edge. This will result in improper contact and possible jamming of the conveyor. Additionally, once the pusher bars are affixed to the electrically conductive conveyor, it is difficult or impossible to adjust the spacing between the pusher bars. Therefore, the spacing between pusher bars must be sufficient to accommodate work pieces with the greatest longitudinal dimension expected to be processed. For all work pieces with longitudinal dimension less than that of the largest work pieces, excessive spacing between the work pieces on the horizontal roller conveyor will occur. This will result in fewer work pieces being processable in any given time period. If the length of the work pieces is greater than the distance between the contactors, they can not be processed at all. If the longitudinal axis of the work pieces is not oriented parallel to the direction of travel, the contactors will not engage the work pieces properly. Furthermore, Spain teaches that the conductive pusher bars accumulate electroplated deposits as they pass through the plating zone. These accumulated deposits must be removed by chemical or electrochemical methods in order to assure proper engagement of the work pieces with the pusher bars. This requires undesirable extra operations and expenses.
Unlike prior art, the embodiments of this invention are mechanically quite simple. There are relatively few total parts and only a few moving parts. Most of the moving parts are subjected primarily to continuous rotation. This type of motion is much less stressful to parts than motions that involve repeated acceleration and deceleration, such as opening and closing of clamps. Roller conveyor mechanisms are extremely durable compared to most other means of transporting work pieces. Therefore, it can reasonably be expected that the time and labor required to maintain the embodiments of this invention will be less than more complex mechanisms.
A primary object of this invention is to electroplate the entire planar surfaces and through hole surfaces of discreet, randomly sized flat work pieces having through holes, such as printed circuit boards, while the work pieces are being transported by a conveyor through a plating bath.
Another object of the invention is to plate the work pieces as they are transferred from conventional conveyorized printed circuit manufacturing equipment without the necessity of unloading the work pieces from the conventional equipment and reloading into the plating apparatus.
Another object of this invention is to allow electrical connection of the work pieces to a power source without deposition of undesirable metallic deposits onto the electrical connecting device.
A still further object of this invention is to minimize the number of moving parts in the mechanism so as to minimize maintenance down time and cost.
A still further object of this invention is to permit the processing of work pieces randomly placed onto the conveyor to avoid the necessity of aligning the parts on the conveyor in order for the electrical contactor to properly engage the work pieces.
A still further object of this invention is to simultaneously electroplate two or more work pieces placed side by side on the roller conveyor.
A still further object of this invention is to be able to electroplate work pieces of differing thicknesses without adjustment of the plating apparatus or with work pieces with differing thicknesses randomly intermixed.
A still further object of the invention is to provide a cathode which more evenly distributes the current over the surface of the board.
Other objects of this invention will become apparent upon reading the detailed description hereinafter following.